In electronic equipments formed of electronic components, heat generated inside must be removed away to cool the interior of the electronic equipments so as to prevent malfunction of the electronic components due to heat. For this purpose, conventionally, air cooling system are widely adopted to cool electronic components, in which a fan is installed inside an electronic device to produce internal air flow to transfer heat generated in a higher-temperature part to a lower-temperature part or to remove heat to outside.
However, such electronic devices as notebook-sized personal computers, and portable information terminals, are constructed to very high degrees of integration for power consumption, reduction, and size and weight reduction. In such highly integrated electronic devices, a space enough to accommodate a fan cannot be ensured to form a heat path for air flow. Hence, instead of the air cooling system in which air flow is caused in a heat path, such devices adopt the heat conducting cooling system in which components in a notebook-sized personal computer are connected to a heat dissipating part through a heat conducting member to transfer heat from a hotter part to the heat dissipating part and discharge heat to the outside.
In this heat conducting cooling system, for example, in order to dissipate heat generated in a CPU from a radiation board, a radiation board made of aluminum is bonded to the CPU with a highly heat conducting adhesive, or a radiation board is pressed against the CPU over a radiation sheet made of a conducting material such as silicone polymer, so as to conduct the heat from the CPU to the radiation board where it is dissipated. In another method, the metal plate of aluminum on the back of the key board is used for a radiation board and the heat is dissipated from the metal plate through a radiation sheet made of silicone polymer.
As stated above, when dissipating heat from a radiation board by thermal conduction, the heat dissipating capability of the radiation board must be increased depending on how much heat would be dissipated. Generally, increasing the heat dissipating capability requires a larger heat dissipating area of the radiation board. However, in most cases, electronic components are fixed in predetermined positions, and therefore the radiation board will interfere with the electronic components if it is simply enlarged to ensure the dissipating area. Then the radiation board must be formed in a complicated shape to avoid interference with the electronic components. Further, in many cases, one unit of radiation board has to be made of two or more radiation parts when it cannot be made of a single radiation part.
In such cases, two radiation parts forming a radiation board are provided, as an integrated radiation board, with a radiation sheet made of silicone polymer etc. interposed between them, or with screws fastening the two radiation parts. If a large number of radiation parts exist in the heat dissipating path connecting a heat generating part and a heat dissipating part, some of the radiation parts may provide lower thermal conductivity, or connective thermal resistance may be developed between the radiation parts, and then the heat resistance of the entire heat dissipating path increases to decrease the heat dissipating capability. If a larger radiation board is used to solve these problems, this will cause a vicious circle of increasing the weight of the electronic equipment. Moreover, when the heat resistance of the entire heat dissipating path is increased, then the heat generated in the heat generating part will be conducted to the surrounding electronic components before dissipated through the heat dissipating path and will exert thermal effects on the electronic components.
When a radiation board made of an aluminum material with poor flexibility is directly attached to a main component such as a CPU or an HDD, vibrations occurring inside and outside of the electronic equipment will be transferred to the CPU or the HDD through the radiation board to damage it.
Further, a radiation board made of metal like copper having superior thermal conductivity to aluminum is heavier. Even for an aluminum radiation board, its weight cannot be neglected from the viewpoint of size and weight reduction. In portable information processors, etc., lighter heat conducting units with efficient heat conductivity are demanded so as to reduce size and weight of main devices.
It is widely known that graphite is most suitable as such a material that can efficiently conduct heat. However, it is very difficult to form graphite into a desired shape; even if a desired shape can be achieved, it is further difficult to ensure strength enough to maintain the shape. In this way, heat conducting units which can keep a fragile material with good heat conductivity like graphite in a desired shape are required for use to form a heat conducting path in a desired shape.